1. Field of the Invention
This invention releates to a positive dielectric anisotropic cyanobiphenyl compound which is useful as a liquid crystal compound.
2. Description of the Prior Art
The positive dielectric anisotropic optically active liquid crystal is used for display element of twisted nematic type and display element of cholestericnematic phase transition type.
The liquid crystal used for above-mentioned display elements is expected to be stable chemically and optically, and expected to show stable state of liquid crystals under the condition from low to high temperature.
However, a compound which gives such conditions satisfaction have apparently not been known, so that several kinds of liquid crystal compound are used as mixture.
For example, it is known that the mixtures of 4-n-alkyl or alkoxy-4'-cyanobiphenyl compound can obtain liquid crystal phase under comparative wide temperature range, however the temperature of crystal-liquid crystal phase transition of these mixtures is more than -10.degree. C., and it can not be satisfactory one.
Moreover, 4-(2-methylbutyl)-4'-cyanobiphenyl is known as a liquid crystal compound which gives cholesteric phase, however, this compound has a demerit, that is to say, the temperature of liquid crystal-isotropic liquid phase transition of this compound is too low (about -30.degree. C.), therefore a quantities of compound are needed to add in order to obtain the aimed property.